1. Field of the Invention
The present invention relates to a dielectric resonator, dielectric filter, duplexer, communication device, and electronic part with a superconductor formed therein which are usable for example in base stations for microwave- and milliwave-band communication equipment.
2. Description of the Related Art
A conventional dielectric resonator is explained with reference to FIG. 9. FIG. 9 is a perspective view of a conventional dielectric resonator.
As shown in FIG. 9, the conventional dielectric resonator 110 is composed of a dielectric body 111 in a cubic shape measuring 22 mm on each edge which is made up of a dielectric material of, for example, a Ba(Sn, Mg, Ta)O3 system. A superconductor 112 is formed on the entire external surface of the dielectric body 111 by screen printing, that is, a thick superconducting film of, for example, 2223 phase of a Bi system. In the dielectric resonator 110 having such composition, the superconductor 112 formed all over the external surface of the dielectric body 111 functions as a shield electrode at a fixed temperature, and forms a resonance space. Furthermore, the unloaded Q of such a resonator 110 is about 30,000 at a frequency of 2 GHz and a temperature of 70 K.
Generally, when a superconductor is used under certain conditions, the surface resistance decreases. For example, the loss of a dielectric filter using a dielectric resonator with a superconductor formed thereon is reduced. Further, in a microstrip-line filter composed of stripline electrodes formed on a dielectric substrate by using a superconductor thin film, when the input power is increased, the loss increases due to the edge effect. According to the dielectric resonator shown in FIG. 9, the electric field is not concentrated at one point and accordingly even if the input power is increased the loss does not relatively increase.
However, there is a problem, in that the quality of the superconductor formed in the vicinity of the edge where two neighboring surfaces join deteriorates in the conventional dielectric resonator. That is, in the superconductor formed in the vicinity of the edge of the dielectric resonator, the surface resistance increases, and because of this effect of the superconductor formed in the vicinity of the edge, a desired Q at no load is cannot be realized upon an increase of the input power, and so on.
Furthermore, in order to find causes of this problem, a study has been done by the inventors. It has been found that the surface resistance of the superconductor is greatly affected by the morphology (geometrical factors such as the size and shape of crystal grains, arrangement of crystal grains, etc.), and it is easy to realize conditions which reduce the surface resistance of the superconductor formed on a flat area, but it is difficult to reduce the surface resistance of the superconductor formed in the vicinity of the edge. Therefore, in the conventional dielectric resonator, the surface resistance of the superconductor formed in the vicinity of the edge increases, and as a result it is difficult to increase the unloaded Q of the dielectric resonator.
Further, generally the mechanical strength of superconductors is low, and another problem is that the superconductor formed in the vicinity of the edge of the dielectric resonators peels off or chips off and the reliability is decreased.
The present invention of an electronic part, dielectric resonator, dielectric filter, duplexer, and communication device was made in consideration of the above-mentioned problems, and it is an object of this invention to present an electronic part, dielectric resonator, dielectric filter, duplexer, and communication device in which the problems are solved, the unloaded Q is increased by suppressing the increase of the surface resistance in the vicinity of the edge, and, further, the reliability of the electrode formed in the vicinity of the edge is increased.
In order to attain the above object, an electronic part according to a first aspect of the present invention comprises a dielectric body in a polyhedral shape, a superconductor formed on at least two neighboring surfaces of the dielectric body, and a metal electrode formed in the vicinity of the edge where the neighboring two surfaces join. The superconductors formed on the neighboring two surfaces are connected by the metal electrode.
Further, a dielectric resonator according to a second aspect of the present invention comprises a dielectric body in a polyhedral shape, a structure in the dielectric body providing a resonance characteristic, a superconductor formed on at least two neighboring surfaces of the dielectric body, and a metal electrode formed in the vicinity of the edge where the neighboring two surfaces join. The superconductors formed on the neighboring two surfaces are connected by the metal electrode.
When the superconductors formed on the neighboring two surfaces of the polyhedral dielectric resonator are connected by the metal electrode formed in the vicinity of the edge where the neighboring surfaces join, the surface resistance in the vicinity of the edge is made lower than the case where the edge is formed by only the superconductors. That is, unlike in a superconductor, in a metal electrode it is considered that the morphology has only a little influence on the surface resistance, even around the edge. Therefore, an electrode having a relatively low surface resistance can be obtained. Further, a metal electrode is higher in mechanical strength and strength of bonding to the dielectric body than a superconductor. Therefore, the reliability of the dielectric body can be improved by preventing peeling off or chipping off of the electrode in the vicinity of the edge in handling the dielectric resonator.
Further, in a dielectric resonator according to a third aspect of the present invention, the superconductor is formed on the entire surface of a polyhedron of a dielectric body. A resonance space is formed by the superconductor formed on the whole surface of the polyhedron and a stable resonance characteristic can be obtained.
Further, in a dielectric resonator according to a fourth aspect of the present invention, the metal electrode is made up of silver or an alloy of silver as a main component. Silver or an alloy of silver as a main component has better bonding characteristics than other metal electrode materials, and further it does not cause any deterioration of the unloaded Q of the dielectric resonator when it is used in the vicinity of the edge.
Further, in a dielectric filter according to a fifth aspect of the present invention, a dielectric resonator according to any one of the second through fourth aspects of the present invention has, in addition, input-output connectors.
Further, a duplexer according to a sixth aspect of the present invention has at least two dielectric filters, input-output connectors connected to each of the dielectric filters, and an antenna connector commonly connected to both of the dielectric filters. At least one of the dielectric filters is a dielectric filter according to the fifth aspect of the present invention.
Further, a communication device according to a seventh aspect of the present invention has a duplexer according to the sixth aspect of the present invention, a transmission circuit connected to at least one of the input-output connectors of the duplexer, and a reception circuit connected to at least one of the input-output connectors which is different from the input-output connector connected to the transmission circuit. An antenna may be connected to the antenna connector of the duplexer.
In this way, a dielectric filter, duplexer, and communication device having low losses are obtained by using a dielectric resonator having a high unloaded Q.
Other features and advantages of the invention will be appreciated from the following detailed description, with reference to the drawings, in which like references in the various figures indicate like elements and parts, and redundant description of like elements and parts is omitted.